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What's all the fuss over "Cam Over"?

Discussion in 'Handloading and Reloading' started by James2, Feb 24, 2012.

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  1. James2

    James2 Well-Known Member

    I believe the term refers to the press ram reaching full up and the lever then goes over center and the ram starts back down. At some point, just over dead center, the lever hits a stop so the lever can go no further. Is this correct to your thinking?

    Well if so, I suggest the cam over point is simply full up for the ram. So what if the lever stops dead center or goes slightly over, the ram cannot go any higher than dead center whether it cams over or not. So why does it even matter?

    Why all the fuss over something that makes absolutely no difference?
  2. R.W.Dale

    R.W.Dale Well-Known Member

    It matters because that cam over point is where you have the greatest mechanical advantage.

    This is important because with difficult to resize cases even the strongest presses will flex upward away from the ram ever so slightly. So if you're not camming the press over against the shellholder and die at the very top of its stroke removing all mechanical play in the system you can very well end up with improperly sized cases.

    In short camming over against the die removes the variable of sizing difficulty from impacting how much sizing you actually get.

    posted via tapatalk using android.
  3. rcmodel

    rcmodel Member in memoriam

    It also matters here on THR when answering newby reloader questions.

    Telling someone to screw the sizing die down until the ram stops, is just asking for them to screw the die down until it stops, and have the ram bumping it before full travel/cam-over is reached.

    Or else they screw the die down to the shell holder with the ram all the way up, and then wonder why they can't chamber the .300 Whizzem after resizing it.

    Adjusting the die for cam-over insures it is set to take all the linkage slop & press frame flex out, and that it is really pushing the case shoulder back where it came from.

    There can be several thousandths difference in a sized case between where the handle stop stops the ram, and where cam-over stops the ram.

  4. fguffey

    fguffey Well-Known Member

    Sugarmaker, again, It is not fair, but, I ask again, if the ROCK CHUCKER cams over’ how much???? in thousands, I have deflection gages, strain gages, in reloading that is just name dropping I understand. RCBS makes a great press, if I thought it had a fault I would build a set of tools that would identify a/the problem.

    Mass Hysteria, it happened when someone with a camera recorded the operation of a RCBS press with out a die and or shell holder, to everyone's horror the ram jumped forward at the top of the stroke and then, the reloading forums took on the nature of MASS HYSTERIA, and then blamed the Chinese, and totally disregarded my advise, “THE Rock Chucker in the video did not cam over” it jammed over, crammed over, etc, but, what ever it did, it did not cam over.

    F. Guffey

    On the light side, a friend, shooter, reloader builder of bench rest type rifles and pistols had a problem, I gathered up a few tools, dies and etc. and went for a visit, he is one of the few people I know that has more presses than I, for heavy work he has a modified A2 RCBS, the A2 RCBS is a cam over press.

    I fixed his problem, when someone builds a rifle that shoots one hold groups it is difficult to impossible to find the problem, again those things do not lock me up. And I assured him nothing I did would improve accuracy.

    Then there are bumpers, “I bump my shoulder .002 etc..” The old presses were designed to bump, I ask those that claim their press ‘bumps’ “by how much, how much when measured in thousands???? and they respond with “My press bumps”.

    Anyhow , it has gotten talked to death, seems, in my opinion, ones opinion is more important to them than giving credit to the design or the person that designed it.

    Back to bump, the cam over when adjusted was a control, when adjusting the die for sizing the ram was raised, the die was adjusted to the shell holder, impossible to grasp, but the difference between top dead center and the ram height after top dead center was the first adjustment before the proverbial 1/4 turn, the difference between the two height was “BUMP”. Now? bump is something reloaders do, and I find impossible, My cases have a tapper, the tapper forms a cone, somewhere out their beyond the cone is an apex, meaning I can not get my die to contact the shoulder without contacting the taper of the case body, shoulder and neck all at the same time, back to adjusting the press to bump.
  5. James2

    James2 Well-Known Member

    I further suggest that if the shell holder is against the die, you can push the casing no further into the die whether it cams over or not. Nor does it matter how much weight you put on the handle, once that shell holder touches that is all you get.

    Yes, you can adjust the die down until you get some resistance at cam over, but all that does is put undue stress on the press. Once that shell holder touches the die with a casing actually in the die, you can't size a casing any more than that. Unless you think you think you can actually crush either the shell holder or die. ??? Believe me when you are sizing cases the " linkage slop & press frame flex" (your words) are already taken out because of the resistance.
    Last edited: Feb 24, 2012
  6. R.W.Dale

    R.W.Dale Well-Known Member

    And this is where you're mistaken as it does not account for the effect of several hundred lbs (wag) of upward force a case going into a sizing die vs a unloaded shellholder with the press in "neutral" condition.

    When sizing the die will get pushed away from where the shellholder is in relation to the die at the top of its travel compared to not sizing anything.

    posted via tapatalk using android.
  7. rcmodel

    rcmodel Member in memoriam

    What he said.

    Frame flex while sizing changes things.

  8. Clark

    Clark Well-Known Member

    That was with a Lee collet neck die in 8x57mm.
    The die was not adjusted correctly [my bad, but RCBS pays the bill]

    RCBS did not just send me a new casting, they sent an entire new press with accessories.

    A year later, the Rockchuckers got bigger where I broke mine.

    I probably put less than 180 pounds of downward force on the ball on the end of the rockchucker handle.
    That would probably break the new ones too.

    I should correct myself. That is not infinite force. The friction keeps it finite.

    Attached Files:

  9. bigedp51

    bigedp51 member

    Buy a "BUMP" die and you won't find it impossible. :rolleyes: If you have a problem with terminology and the English language you might want to find another hobby. ;)


    Long ago in high school English class our English teacher told the story of a well known 17 century British author. The well known British author was attending a play but was in bad need of a bath.

    The woman seated next to him told the British author “You smell” the British author replied “No madam, you smell, I stink” :eek:

    Cam over and bump do not smell or stink when used properly but misunderstanding the English language and complaining about it has an odor all its own. In other words fguffey something smells here and it isn't my reloading press.
    Last edited: Feb 24, 2012
  10. popper

    popper Well-Known Member

    So what does the continual application of the extra 20-30# force applied to non-lubed (linkage pins) steel do after a few thou cases? And the alum alloy used in presses? Much less the threaded alum. As Fguffy says, the cam-over is about .003.
  11. bigedp51

    bigedp51 member

    You could have ten different reloading presses and ten different reloaders pulling the handle and get ten different cam over readings.

    In another forum a poster said he attached a click adjustable torque wrench to his press to get uniform results.

    My reply was "I can't get the handle thingy to click, now what do I do?" :rolleyes:


    We now have a new reloading word.............torque over :rolleyes:
  12. Hopkins

    Hopkins Well-Known Member

    Makes me want to buy an arbor press but who makes a fl sizing die for for an arbor press? How would you get the case out of the die after wards?
  13. rcmodel

    rcmodel Member in memoriam

    I don't know yet.

    I've only been adjusting bottleneck rifle sizing dies to cam over since 1970 in my old RCBS RockChucker.

    I'll let you know if I ever wear it out.
    But it's very unlikely I will live that long.

  14. cfullgraf

    cfullgraf Well-Known Member

    One can see the effect of the loosemess in the press' linkage system by doing the following.

    Raise the ram to the top and screw the sizing die down hard against the shell holder. lock the die down.

    Now insert a case to be sized. At the top of the stroke, you will see a sliver of light between the die and the shell holder.

    A torque wrench would at lease allow one to apply the same force to the ram with every stroke.
  15. p5200

    p5200 Well-Known Member

    I've noticed when I reload my 9mm. rounds using once fired brass, the bullet shows a pretty good bulge in the case. When loading new brass there's no bulge at all usually. Should I be adjusting my LEE Carbide sizing die with a little cam over or, could that even be the cause of the bulge? I'm using all the dies in the 4 die set. :)
  16. rcmodel

    rcmodel Member in memoriam

    The 9mm has a tapered case.

    With a steel die, the further down you screw the die, the more sizing it gets.

    But, most carbide dies are not tapered, so if you size the neck enough, the base gets sized more then enough, and you will get what you describe.

    It is actually a sign of good neck tension, and is a Good Thing, as it should totally prevent bullet set-back during feeding.

  17. p5200

    p5200 Well-Known Member

    Thanks for the info!
  18. rsrocket1

    rsrocket1 Well-Known Member

    If you know exatly how much the press cams over, you are OK. The problem is you don't know how much slop there is in the press so that when it's at the top of the stroke, it is no longer at the same point exerting the same pressure when under a load. On a non-cam over press, when you press with 25 pounds of force after it stops, you know that you put the same pressure on the die. You'll never know with a cam over press.

    My Lee Challenger press does not cam over and I like using it for neck sizing .308 or even "partial full lenght resizing" where I use a full length resizing die to bump the shoulder back to a point less than what a full length resizing job does. I can get the feel of how much to press on it to get enough neck tension without going overboard.

    My LnL AP cams over. It is not good for bolt action rifle rounds, but it is fine for straight walled pistol rounds so long as I don't have to ensure complete full length resizing of "Glocked" brass.

    For pistol rounds or plinking and blasting with rifle reloads, cam over is nothing to worry about.
  19. bigedp51

    bigedp51 member


    You can see below having .004 between the shell holder and the bottom of the full length die using headspace control shims and no hard cam over on my 40+ year old Rock Chucker press was the cause of my excessively large groups below. :rolleyes:


    Eat your heart out fguffey. :neener:
  20. ranger335v

    ranger335v Well-Known Member

    "..I suggest the cam over point is simply full up for the ram. So what if the lever stops dead center or goes slightly over, the ram cannot go any higher than dead center whether it cams over or not. So why does it even matter?"

    You're absolutely correct. The press 'cams over' when we lower the lever weither or not there's die in the press. Cam-over has taken on near magical but fuzzy proportions in a lot of people's minds.

    "Why all the fuss over something that makes absolutely no difference?"

    Beats me. The only good thing about camming over is the tactile feedback confirming we have indeed raised the ram/case as high as it can go.

    How we should set the dies is a whole different thing and that too seems to be grossly misunderstood by those who seek a rote die adjustment process they can follow without having to understand what they're doing or why.
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